A plane at right angles to the principal axis of a lens or mirror on which the best image of an object is focused. A term used to describe the capacity of objective lenses to receive light. For example, doubling the diameter of the objective, quadruples the light gathering power. Light Transmission. All these factors affect brightness: objective lens diameter, magnification, the type and quality of the objective lens glass and the type of lens coatings. The percentage remaining is light transmission.
Magnification is the degree to which the object being viewed is enlarged. For example, with a x riflescope, you are able to magnify the object or target from 3 to 15 times bigger that it would appear with the human eye. The level of power also affects the brightness of an image and field of view, so at lower power, the image will be brighter and the viewing area will also be larger. A unit of angular measure that is subtended by one unit of length at a distance of 1, units of length, such as one meter at a distance of 1, meters.
The spaces between dot centers on mil dot reticles subtend 3. Minute of Angle. Minute of Angle MOA is a unit of measurement of a circle, and is 1. For all practical purposes it is called 1 inch at yards. It is 2 inches at yards, 5 inches at yards, one half inch at 50 yards, etc. Objective Lens. The objective lens of a riflescope is the front lens. The diameter of one of the lens is typically measured in millimeters. It is the last number listed in the product description. For example, a x56 will have a 56mm objective lens.
The diameter of the lens determines how much light is delivered to your eye. A larger lens translates into greater detail and image clarity. This is especially useful in low light conditions such as dawn and dusk. Ocular Lens. The ocular lens is the lens closest to your eye. I try to make note of the more commonly asked questions, in an effort to put the answer at least my interpretation of the answer down on paper.
By far the most common questions I hear in person and am asked via email off this web site are focused on rifle scope magnification and how to read scope numbers. Before I get into the answer, let me provide some basic background information about rifle scopes so my answer makes more sense. Without getting overly technical, rifle scope magnification is measured against what the naked eye sees.
So, a scope adjusted to 4 power would magnify to 4 times what the naked eye can see. A scope adjusted to 24 power would magnify 24 times what the naked eye can see. By that, I mean that scopes from every country or geography use the power magnification as compared to the naked eye approach. A fixed power scope is a scope that has a fixed or non-adjustable magnification setting.
And when I say simplistic, I mean that they were basically look through the scope and shoot as they did not offer any adjustment of any kind. Fixed powered scopes featured a magnification that ranged from as low as 2. The most popular fixed power models were the 4x, 6x, and 8x models. When adjustable power scopes hit the market and became more affordable, the fixed power scopes started to fall out of popularity.
Variable power scopes feature a magnification range that can be adjusted from one power to another. The magnification adjustment is done via a power adjustment ring, located on eye piece, that rotates.
The eye piece is marked with numbers that corresponds to the power magnification. An erector assembly contains two lenses that flip the image so that it is right-side-up. The erector assembly can also contain the additional magnifying lenses for a variable magnification scope. Focus the image: The ocular lens focuses the image that has been magnified and flipped right-side up for your eye. The diameter of the ocular lens also determines the eye relief — the distance between the scope and your eye from which you can see the full, focused image.
Physical Limitations of Magnifying Lenses Magnification does come with trade-offs. Chromatic Aberration Chromatic aberration or fringing can occur with any lens, but worsens as magnification increases. Field Curvature In scopes with low magnification, field curvature can cause blurriness at the edges of the image. Spherical Aberration As magnification increases, spherical aberration may arise. Field of View Field of view can be calculated by dividing the diameter of the objective lens by the magnification.
Dimness As lenses thicken, or more lenses are included in the scope, more light will be reflected and absorbed rather than transmitted. Making a Choice — Rifle Scope Magnification vs. Distance There is a saying that you should choose the magnification that is just enough for you to hit the target. Share this article.
Shop This Article. Fully Multi Coated - Multiple layers of anti-reflective coating on all air-to-glass surfaces deliver bright, high-contrast images. For instance, a typical 3x variable scope might have a FOV at yards of a bit over 30 feet, and at 9x, the FOV would be around 14 feet.
A larger objective lens diameter will not change these figures. Field of view is directly related to the construction of the eyepiece. Another trend today is the sale of anything called "tactical. Real military snipers use top-quality fixed 10x scopes most often.
These have mil-dot reticles that, in the hands of a practiced individual or team of two, often with calculators and knowing the approximate size of their target, can estimate distance and hold-over or elevation clicks. Almost all mil-dot calculations must be made with scopes at their highest power.
Fixed power scopes eliminate miscalculations by having a scope set at less than its highest power. The "mil" in mil-dot does not mean military. It means milliradian , a unit of measurement, and is about 3. Stateside law enforcement agencies most often use variable scopes of the highest quality, and mil-dot type reticles are not often used. They clutter the field of view, and the longest shots almost ever taken are across a street, well under yards.
Range estimation with a reticle is never required. Mil-dot reticles in most people's scopes are nothing but a gimmick and an added expense. They will never use them the way they were designed, which is fine. You can still use them in the field to more accurately estimate hold-over at distances, especially for prairie dogs or plinking, or just because you want it.
The reticles in a mil-dot do subtend cover more of your target than necessary, though. But buy what you like for any reason. You don't have to buy or not buy something because of someone else's opinion, or use it as designed. High-quality scopes are repeatable. That is, if you adjust your windage and elevation dials for point of impact at one setting, then move them around and shoot in different places, then back to the original place, the point of impact will be the same as it was when you started.
Good quality scopes will also move the point of impact when you adjust your dials, without having to "settle in. Sadly, more often than not, lesser quality scopes won't do this without shooting a few times first, to "settle in" the scope's internal adjustments. Some people "tap" on their scope with a coin or cartridge case to help this process.
But repeatability is not that important in many scopes. Generally, you will sight in a rifle and leave it alone except for minor adjustments required due to changes in ammunition type. If you have a. This is a unit of measurement of a circle, and is 1.
For all practical purposes, it is called 1 inch at yards. It is 2 inches at yards, 5 inches at yards, one half inch at 50 yards, etc.
The turrets are housed in the center of your scope tube in a protrusion called the turret housing. The turrets are sometimes made to be turned with a coin, and sometimes they are finger adjustable. Target turrets are tall, and the clicks are easily seen and felt. Target turrets are most suited to use where they won't get banged around or snagged on gear or brush. This is why hunting scopes don't have them, and instead are much lower profile.
The turret caps are often sealed with an "O" ring, and help prevent moisture and debris from entering the scope through its weakest parts. Many scopes now have large dials, but with locking adjustments, to prevent their inadvertent movement.
Most turrets also have a way to move or remove a turret or portion of a turret to correspond to zero after you sight it with a particular load.
At the turn of the century, BDC dials and reticles were often set for just a few cartridges, like 5. Atmospheric conditions are varied, but the BDC dials stayed the same regardless of cartridge velocity, projectile BC ballistic coefficient , temperature, barrel length, or elevation.
They were ballpark, not precise, except for rare cases. Enter the Nikon "Spot On Technology" website. This appeared in the mids, and was my favorite new product at the Vegas Shot Show that year. It is simply amazing. Just enter in any cartridge's ballistic information, whether factory or hand-loaded, and get the trajectory for that cartridge with any type of atmospheric information. It is used to find the distances that the Nikon BDC reticle circles line up with at any magnification.
It will also work with any crosshair scope from any company. You can even print it out for reference or size it to be taped to your stock or scope for quick reference in the field. Since "Spot On", many other companies have developed their own programs that have similar attributes. Some are very good, some are a bit heady and complicated. These programs are the most valuable development in riflescope use in decades and have the most to do with hunters' ability or desire to take longer shots than ever before possible.
Whether you move a turret to adjust for distance, or use the stadia lines or circles in your reticle, these are here to stay, and a lot of the guessing game is completely gone. Used with skill and a laser rangefinder, these reticles and websites combine to make you feel quite empowered.
They presume the shooter is capable of making ethical shots in the field, and the only way to ensure this is to burn powder with trigger time and good practice, not just shooting. For further information on reticles, take a look at our Advanced Reticle Guide.
If your scope is correctly mounted, using a boresighter should get you close enough to print a bullet hole on a large target at 50 yards. No boresight, even a laser boresight, will sight in your gun for you. You must shoot the gun and adjust your scope accordingly to sight it in.
Every gun is an individual. No two are alike, even if the serial numbers are consecutive. If a particular gun shoots a certain kind of ammunition well, there's absolutely no guarantee that an identical gun will like it at all.
If you mount a good scope on a good gun with good rings and bases , and find a certain kind of ammo that it shoots well, with a bullet that serves your purposes well, YOU WIN! Buy a case of the same exact ammo with the same lot number, keep it with the gun, and don't change a thing. Also, your scope is at its strongest when your windage and elevation adjustments are in the center of the available adjustment range.
This is called mechanical zero. When you buy a scope, turn the dials all the way one way and then the other, counting how many full and partial turns, then split that number and find the middle. Start there for your adjustments. Many rear bases have windage adjustments. Use them.
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